Prior to first use, and periodically thereafter, electronic circuit automated test equipment (ATE) needs to be calibrated to ensure that manufacturing variances in its signal paths, environmental conditions under which a device under test (DUT) is tested, and other factors, are taken into account when interpreting test data obtained from the ATE.
Typically, calibration comprises 1) sequentially connecting a reference channel of the ATE (e.g., a master clock source) to each of the other channels of the ATE, 2) transmitting a test signal after each sequential connection, and then 3) recording a characteristic of each transmitted test signal (e.g., recording a signal delay).
Traditionally, ATE has been calibrated using mechanical robots or relay matrices that sequentially connect the ATE's reference channel to each of the ATE's other channels. However, these solutions tend to be very expensive and require a significant amount of time to complete calibration. Furthermore, they usually undertake calibration in a “calibration environment” that may differ from a production test environment. For example, the calibration environment will typically not include a probecard (i.e., the custom interface that is designed to connect the ATE to a particular DUT (or DUT set) during production test).
Another way to undertake ATE calibration is via a custom-fabricated semiconductor wafer. The custom wafer may include more or less active circuitry (e.g., switching matrices), but in a simple embodiment merely comprises a plurality of custom dies, each of which has one or more pairs of pins that are interconnected via a circuit trace (or traces). An advantage of using a custom wafer is that it can be mounted to ATE similarly to a production wafer, thus enabling the calibration of ATE in light of probecard signal paths. However, custom-fabricated semiconductor wafers also tend to be very expensive, and their useful lives can be short (e.g., often, as a result of repeated probing, their die pads wear, leading to loss of die pad consistency and poor connectivity with ATE channels).